The stable isotope amount effect has often been invoked to explain patterns of
isotopic composition of rainfall in the tropics. This paper describes a new approach,
correlating the isotopic composition of precipitation with cloud height and atmospheric
temperature using NEXRAD radar echo tops, which are a measure of the maximum
altitude of rainfall within the clouds. The seasonal differences in echo top altitudes and
their corresponding temperatures are correlated with the isotopic composition of
rainfall. These results offer another factor to consider in interpretation of the seasonal
variation in isotopic composition of tropical rainfall, which has previously been linked to
amount or rainout effects and not to temperature effects. Rain and cloud water isotope
collectors in the Luquillo Mountains in northeastern Puerto Rico were sampled monthly
for three years and precipitation was analyzed for d18O and d2H. Precipitation enriched in
18O and 2H occurred during the winter dry season (approximately December–May)
and was associated with a weather pattern of trade wind showers and frontal systems.
During the summer rainy season (approximately June–November), precipitation was
depleted in 18O and 2H and originated in low pressure systems and convection associated
with waves embedded in the prevailing easterly airflow. Rain substantially depleted in 18O
and 2H compared to the aforementioned weather patterns occurred during large low
pressure systems. Weather analysis showed that 29% of rain input to the Luquillo
Mountains was trade wind orographic rainfall, and 30% of rainfall could be attributed to
easterly waves and low pressure systems. Isotopic signatures associated with these
major climate patterns can be used to determine their influence on streamflow and
groundwater recharge and to monitor possible effects of climate change on regional water
resources.

The Toa Baja Well was drilled on the coastal
plains of northern Puerto Rico with a total depth of 2705m
[Larue, 1990]. Interstratified limestone, quartz-bearing
calcareous sandstones, and shales dominate the uppermost 580
m and are separated from underlying rocks by an
unconformity. Below this unconformity continuing tototal
depth, lithologies encountered consist of volcaniclastic
sandstones/siltstones, pelagic carbonates, volcanic flows and
either plutonic rocks or coarse-grained immature sandstones
derived from plutonic bodies....

Annually resolved coral delta O-18 and Sr/Ca records from southwestern Puerto Rico are used to investigate Caribbean climate variability between 1751 and 2004 C. E. Mean surface ocean temperatures in this region have increased steadily by about 2 degrees C since the year 1751, with Sr/Ca data indicating 2.1 +/- 0.8 degrees C and delta O-18 data indicating 2.7 +/- 0.5 degrees C. Coral geochemical records from across the tropics demonstrate that regional variability is important for understanding climate variations at centennial time scales. A strong multidecadal salinity signal in the oxygen isotope data correlates with observed multidecadal temperature variations in the Northern Hemisphere. Instrumental wind and precipitation data indicate that the most recent coral isotopic variations are caused by expansion and contraction of the steep regional salinity gradient, forced by trade wind anomalies through meridional Ekman transport. The timing of the fluctuations suggests that the multidecadal-scale wind and surface circulation anomalies might play a role in Atlantic temperature variability and meridional overturning circulation, but further work is needed to confirm this suggestion.